exploration

Unconventional Methods For Unconventional Plays: Using Elemental Data To Understand Shale Resource Plays Ken Ratcliffe and Milly Wright, Chemostrat; Dave Spain, BP USA

Part 1 equivalent resources of , Mexico and Wright et al., 2010). Published accounts using hales are an important hydrocarbon the United States and it exceeds the estimated this approach are largely on fluvial successions, resource; yet understanding them as recoverable reserves of CSG in Australia. where stratigraphic correlation using traditional S reservoirs remains problematic. Their techniques are often problematic (e.g. Pearce fine-grained, organic-rich yet superficially Despite the activity and the large number of et al., 2005, Ratcliffe et al., 2006, Ratcliffe et homogenous character make the application well completions, the fine grained, macro-scale al., 2010, Wright et al., 2010 and Hildred et al., of traditional reservoir characterisation homogeneity of many formations currently 2011). Over the same decade, inorganic whole methods impractical or impossible. being exploited in North America negates some rock geochemical datasets have routinely been Increasingly, in the North American shale of the more traditional approaches to reservoir acquired from mudrocks, the data typically plays, inorganic geochemical data are being characterisation and stratigraphic correlation, being used to help elucidate paleoredox used as a one-stop method for understanding which has resulted in the search for new conditions during oceanic anoxic events (e.g. shale reservoirs. For decades, elemental data methodologies that enable better stratigraphic Tribovillard et al., 2006, Turgen and Brumsack, have been used to help solve stratigraphic understanding of shale reservoirs. Here, the 2006, Tribovillard et al., 2008, Negri et al., problems, i.e. definition of chemostratigraphic application and potential of one approach 2009, Jenkyns, 2010). Here, approaches of the frameworks. However, the same dataset is demonstrated, namely the application of chemostratigrapher and the oceanic anoxic acquired for chemostratigraphic studies can inorganic whole rock geochemical data (or event are combined and pragmatically applied be used to model shale mineralogy, model chemostratigraphy) to shale resource plays. to plays in North America. TOC levels, determine paleoredox conditions, identify zones of biogenic silica in and Inorganic whole rock geochemical data have While the applications presented here are largely provide information about transgressive – been used to define stratigraphic correlations tested on the Haynesville Formation and, to a lesser regressive cycles. in the petroleum industry for over a decade extent, the Eagle Ford and Muskwa formations, now (Ratcliffe et al., 2010 and references cited the approaches adopted herein would be equally The applications of elemental data to therein). The technique of chemostratigraphy applicable to any shale resource play. understanding shale plays fall into two natural relies upon recognising changes in element groupings. The first is the traditional use of concentrations through time and using those Methodology and dataset geochemical data to aid in understanding to model changes in geological features, such regional and reservoir-scale stratigraphy. This as paleoclimate (Pearce et al., 2005, Ratcliffe et The data for this article are largely from the application is discussed in this issue of PESA News al., 2010) and provenance (Ratcliffe et al., 2007, Haynesville Formation, with less extensive datasets Resources. The second main use geochemical data is in modeling applications, such as those listed above, and this will be discussed in the next issue of PESA News Resources.

Introduction

In the past decade, shale resource plays have risen to the forefront of hydrocarbon exploration, as shown by the numerous 'shale conferences' in the past two years alone (Critical Assessment of Shale Resource Plays, Hedberg Research Conference Dec 2010, Austin, Texas, World Shale Gas Conference & Exhibition, Nov 2010, Dallas Forth Worth, Texas, Nov 2011, Houston, Texas, Global Unconventional Gas Conference, June 2010, Amsterdam, Shale Gas World Europe, Dec 2010, Warsaw, Poland, Shale Gas Insight 2011, Nov 2011 Philadelphia, Pennsylvanian, Shale Gas Asia 2011, Feb, New Delhi, India to name but a few). Although the majority of active producing shale plays are in North America, the success there has led to increased interest in shale formations around the world, including in Australia, where according to a June 2011 report commissioned by the US Energy Information Agency, Australia has 396 Tcf of technically recoverable shale gas resources. This is equivalent to about 20% of the combined Fig. 1. Geographic location and ages of the shale reservoir plays referred to in the text.

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from the Muskwa Formation and the Eagle Ford Formation also being drawn upon (Figure 1). All TERREX GROUP of these formations are proven shale gas plays, with each being extensively drilled for exploration, appraisal and production.

The Haynesville Formation is Terrex Seismic Terrex Contracting late (Kimmeridgian) in 2D, 3D & 4D Seismic Data Acquisition Seismic Line Preparation & Restoration age. It is a locally calcareous and Australia’s most Australia’s Largest Onshore Fleet Minimal Environmental Impact organic rich (TOC values are technologically 2-6%) mudrock that occurs in northeast Texas and northwest Terrex Geophysical Terrex Spatial innovative and Louisiana (Figure 1). It was 2D, 3D & 4D Planning & Design GPS, GIS Surveying experienced deposited in an extensive intra shelf basin on the young, In-field Processing & QC Seismic, Gravity, Geodetic Surveys providers passive margin of the US Gulf Digital Terrain Modelling & Hi-Res LiDAR of seismic Coast during a period of arid climatic conditions. Basement Fig. 2. Geochemical characterisation of the Haynesville Formation as penetrated in Well Watson-4. Logs for a series of key exploration faulting and salt movement elemental ratios are plotted relative to depth in order to characterise broad scale “Chemostratigraphic Packages” (Plot services controlled the initial water depths, A) and finer scale geochemical units Plot B). All samples analysed here are from conventional core and all data were resulting in regions of the sea bottom acquired using ICP OES MS with a Li-metaborate fusion preparation. having restricted communication with the open ocean and therefore palynomorphs are often thermally degraded. • Package 3 (transitional between the recurrently experiencing anoxic bottom water Also, electric log correlations are hampered by Haynesville and Bossier formations) is conditions. The Eagle Ford Formation is a dark the variable controls on U, K and Th. In typical identified by generally lower Fe2O3/MgO grey calcareous, locally organic-rich mudstone fluvial and shallow oxic marine settings the K, Th, and Rb/K2O values compared to Package of Cenomanian – Turonian age (Figure 1). It and U are all largely controlled by the amount 2 and lower Th/U values compared to sub-crops in south Texas forming a narrow strip of clay versus sand, enabling lithostratigraphic Package 4.This interval also displays that is 150 miles long. Over this distance, the and sequence stratigraphic correlations to be elevated CaO/Al2O3 values relative to Eagle Ford Shale Formation varies in thickness made from the gamma logs. However, in the Packages 2 and 4. from approximately 75 ft to 300 ft. The Muskwa Haynesville Formation, U is associated with Formation is () in age and is TOC and minerals derived from authigenic • Package 2 (equivalent to the Haynesville located in , northeastern British enrichment in anoxic conditions, whereas Formation) is characterised by higher

Colombia and in the southern portion of the K and Th are associated with the amount of Fe2O3/MgO values than underlying , Canada (Figure 1). terrigenous-derived material. These associations packages and lower Th/U and MgO/ are discussed in greater detail in Part 2 of (CaO+MgO) values than the overlying All data for this article have been acquired using this article. Therefore, using gamma logs for Package 4. Inductively Coupled Plasma Optical Emission stratigraphic correlations in shale gas plays is (ICP-OES) and Mass Spectrometry (ICP-MS), enigmatic. Furthermore, the apparent macro- • Package 1 (transitional between the following a Li-metaborate fusion procedure scale homogeneity of the mud-rocks precludes Haynesville and Smackover formations)

(Jarvis and Jarvis, 1995). These preparation and the recognition of sedimentary facies that can is characterised by CaO/Al2O3 values that analytical methods provide data for 10 major be used for stratigraphic correlations, particularly are intermediate between those of elements (SiO2, TiO2, Al2O3, Fe2O3, MgO, MnO, when only cuttings samples are available. Packages 0 and 2, and lower Fe2O3/MgO

CaO, Na2O, K2O, P2O5), 25 trace elements (Ba, Be, values than overlying packages. Co, Cr, Cs, Cu, Ga, Hf, Mo, Nb, Ni, Pb, Rb, Sc, Sn, Chemostratigraphy has been used to Sr, Ta, Tl, Th, U, V, W, Y, Zn, and Zr) and 14 rare characterise and correlate the Haynesville • Package 0 (equivalent to the Smackover earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Formation, along with underlying and Formation) is identified by high CaO/Al2O3 Ho, Dy, Er, Tm, Yb, and Lu). overlying portions of the Smackover and ratios. Bossier formations respectively. Figure 2 Stratigraphic applications of shows a chemostratigraphic package and It is possible to further subdivide the unit level characterisation of the Haynesville Haynesville Formation (Chemostratigraphic whole rock inorganic geochemical Formation in a single well. On Figure 2a the Package 2) into a series of higher resolution data in shales study intervals are divided into a series of Chemostratigraphic Units; 2.1, 2.2, 2.3 and Developing stratigraphic frameworks is the first order Chemostratigraphic Packages, 0-4, 2.4 (Figure 2b). These units are defined pertH HeaD Office BrisBane OperatiOns Office qUeensLanD reGiOnaL spatiaL Office key to the exploration and exploitation of any based on changing values of CaO/Al2O3, Rb/ by more subtle geochemical variations Level 4, 76 Kings Park Rd 22 Crockford St PO Box 713 formation in any hydrocarbon basin. In shale K2O, Fe2O3/MgO, Th/U and MgO/(CaO+MgO): in CaO/Al2O3, Rb/K2O, Fe2O3/MgO, Th/U, West Perth WA 6005 Banyo QLD 4014 Yeppoon QLD 4703 plays, the more traditional methods used MgO/(CaO+MgO) and Zr/Nb ratios. The to define stratigraphic correlations in the oil • Package 4 (approximately equivalent to resultant Chemostratigraphic Package and T +61 8 9235 4600 T +61 7 3621 0300 T +61 7 4939 2866 Health & Safety Environment industry are somewhat limited. Commonly, the the Bossier Formation) is identified by Chemostratigraphic Unit correlations are F +61 8 9324 3640 F +61 7 3266 7345 F +61 7 4939 2867 OHSAS 18001 ISO 14001 E [email protected] E [email protected] E [email protected] restricted basin nature of their accumulation higher Th/U and MgO/(CaO+MgO) values displayed on Figures 3 and 3b for wells Terrex Seismic is certified to OHSAS 18001, can limit the use of biostratigraphy, and than underlying packages. Watson-4, Glaspie Ocie GU-10, George T.W. www.terrexseismic.com ISO 14001 and AS 4801.

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another, the more closely linked they are in the sediment. It is apparent from Figure 5 that the elements fall into three broad groups:

• Group 1 elements include CaO, MgO, MnO and Sr, a grouping of elements associated with carbonate minerals such as calcite and dolomite.

• Group 2 elements include Mo, U, Ni, V, Cu, Zn and Co. These are all elements associated with authigenic enrichment under anoxic conditions (Tribovillard et al., 2006).

• Group 3 elements contain almost all other elements and are associated with terrigenous minerals, including clay

minerals (e.g. Al2O3, K2O, Th), quartz (SiO2),

feldspars (Na2O) and heavy minerals (e.g. Zr, Hf).

The significance of these element groupings will be discussed further in Part 2 of this article.

Conclusions

Fig. 3. Correlation of wells Watson-4, Glaspie Ocie GU-10, George T.W. GUA- In this first look at the application of elemental 8H, CGU 13-17 and Johnson Trust 1-2H based on the geochemical criteria data to helping develop shale resource defined in Figure 2. Plot (A) shows the correlation of “Chemostratigraphic plays, the 'traditional' use of elemental data Packages” and includes data from the formations over and underlying the for chemostratigraphy and its extension to Haynesville Formation. Plot B focuses only on the Haynesville Formation and high resolution definitions for placement of shows the correlation of “Chemostratigraphic Units” within this formation. well-bores has been described. In the next Inset map shows relative positions of well in correlation panels. part of the article, the more unconventional applications of mineral and TOC modelling,

GUA-8H, CGU 13-17 and Johnson Trust 1-2H. the TiO2/Nb increases, with the unit 2.3 / 2.2 identification of biogenic silica, recognition of boundary (base of target zone) being defined transgressive-regressive cycles and modelling

High resolution stratigraphic by a decrease in TiO2/Nb values and an increase of paleoredox conditions will be discussed. applications of whole rock in P2O5 values (Figure 4). By analysing cutting inorganic geochemical data in samples from the horizontal offset to the References shales vertical hole the point at which the well bore enters the target zone is clearly defined by the Ellwood, B.B., Tomkin, J.H., Ratcliffe, K.T., Although high resolution stratigraphic sharp increase in P2O5 values around 15,800’ Wright, A.M. and Kafafy, A.M. 2008. Magnetic frameworks are always desirable, the need (MD). Susceptibility and Geochemistry for the for them is exacerbated in shale plays by the Cenomanian/Turonian Boundary GSSP with 3 increased use of horizontal drilling in their Geochemistry and mineralogy Correlation to Time Equivalent Core. Palaeo , exploitation. Typically, the horizontal leg of a v. 251, p. 1–22. well will be several thousand feet in length, The key to fully utilising major and trace with the aim of remaining in a thin stratigraphic element changes in any ancient sequence is Hildred, G.V., Ratcliffe, K.T. and Schmidt, K., horizon over as much of that distance as understanding the geological controls on each 2011. Application of Inorganic Whole-Rock possible. Figure 4 schematically shows how of the elements (Ratcliffe et al., 2007, Hildred Geochemistry to Shale Resource Plays: an the well-bore pathway through the Eagle Ford et al., 2011, Wright et al., 2010). A simple, but Example from the Eagle Ford Shale, Texas. Formation in a 'horizontal' sidetrack well can effective way to achieve this is the consideration Houston Geological Society Bulletin, April, 2011. be related back to the pilot hole by analysis of of the Eigen-vector (EV) scores calculated cuttings samples. The ideal target zone for this when PCA (principal component analysis) is Jarvis, I. and Jarvis, K.E. 1995. Plasma lateral well through the Eagle Ford Formation carried out on a geochemical dataset (Pearce spectrometry in earth sciences: techniques, is coincident with the geochemically defined et al., 2005, Svendsen et al., 2007; Ellwood et applications and future trends; In Jarvis, I., and Unit 2.3 (Schmidt et al., 2010). At the top of al., 2008; Pe-Piper et al., 2008, Ratcliffe et al., Jarvis, K.E., eds., Plasma Spectrometry in Earth top Unit 2.3 (the top of the target zone) there 2010). One Figure 5, EV1 and EV2 scores, which Sciences: Chemical Geology, v. 95, p. 1–33. is a very marked downhole increase in P2O5 together account for 73% of the variation within values, together with an increase in TiO2/Nb the entire Haynesville Formation dataset, are Jenkyns, H.C. 2010. Geochemistry of oceanic and decrease in Th/U values. From the top of plotted. On cross-plots such as that displayed on anoxic events. Geochemistry Geophysics this unit to its base, the P2O5 decreases and Figure 5, the more closely elements plot to one Geosystems, v. 11, p.1–30.

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fluvio-eolian setting using elemental whole- rock geochemistry—applications for reservoir characterisation. Journal of Sedimentary Research, v. 77, p. 23–33.

Tribovillard, N., Bout-Roumazeilles, V., Algeo, T., Lyons, T.W.; Sionneau, T., Montero-Serrano, J.C., Riboulleau, A. and Baudin, F. 2008. Paleodepositional conditions in the Orca Basin as inferred from organic matter and trace metal contents. Marine Geology, v. 254, p. 62–72.

Tribovillard, N., Algeo, T., Lyons, T.W. and Riboulleau, A. 2006. Trace metals as paleoredox and paleoproductivity proxies; an update 2006. Chemical Geology, v. 232, p. 12–32.

Fig. 4. Using geochemical data to determine the well-bore pathway of a horizontal well relative to the Turgeon, S. and Brumsack. H.J. 2006. Anoxic stratigraphy of the vertical pilot hole in the Eagle Ford Formation, Texas. Left hand panel displays the vs. dysoxic events reflected in sediment chemostratigraphic zonation of a vertical hole through the Eagle Ford Formation. Samples analysed in the geochemistry during the Cenomanian–Turonian vertical hole are a mixture of core and cuttings. The right hand panel displays the chemical variations in a “horizontal” sidetrack identified by analysis of cuttings samples. Diagram redrawn from Ratcliffe et al., (2011) Boundary Event () in the Umbria– Marche Basin of central Italy. Chemical Geology v. 234 p. 321–339. Negri, A., Ferretti, A., Wagner, T. and Meyers, P.A. offshore Northwest Australia. APPEA Journal 2009. Organic-carbon-rich sediments through 2010 50th Anniversary Issue p. 371–385. World Shale Gas Resources: An Initial the Phanerozoic; processes, progress, and Assessment of 14 Regions Outside the United perspectives. Palaeo3, v. 273, p. 302–328. Ratcliffe, K.T., Hildred, G.V., Schmidt, K. and Wright, States, prepared by Advanced Resources A.M. 2011. High resolution chemostratigraphy for International for the U.S. Energy Information Pe-Piper, G., Triantafyllidis, S. and Piper, D.J.W. delineating well-bore pathways in the Eagle Ford Administration, April 2011. 2008. Geochemical identification of clastic Formation of Texas, USA. Scandinavian Oil and sediment provenance from known sources of Gas Magasine, No. 3/4, p. 62–65. Wright, A.M., Ratcliffe, K.T., Zaitlin, B.A. similar geology: the Cretaceous Scotian Basin, and Wray, D.S. 2010. The application Canada. Journal of Sedimentary Research, v. 78, Schmidt, K., Poole, M., Hildred, G. 2010. A of chemostratigraphic techniques to p. 595–607. Triumvirate of Targeting — A Three-Pronged distinguish compound incised valleys in low- Approach to Keeping a Horizontal Well in accommodation incised-valley systems in a Pearce, T.J., Wray, D.S., Ratcliffe, K.T., Wright, D.K. the Desired Eagle Ford Reservoir Interval. foreland-basin setting: an example from the and Moscarello, A. 2005. Chemostratigraphy of American Association of Petroleum Geologists, Lower Cretaceous Mannville Group and Basal the Upper Schooner Formation, International Annual Convention & Exhibition Colorado Sandstone (Colorado Group), Western southern North Sea. In: Carboniferous September 12–15, 2010. Canadian Sedimentary Basin. In: Ratcliffe, K.T. hydrocarbon geology: the southern North Sea and Zaitlin B.A. eds Application of Modern and surrounding onshore areas; In Collinson, Svendsen, J., Friis, H., Stollhofen, H. and Hartley, Stratigraphic Techniques: Theory and Case J.D., Evans, D.J., Holliday, D.W. and Jones N.S. N. 2007. Facies discrimination in a mixed Histories SEPM Sp Pub. No. 94. P. 93–109.  eds. Yorkshire Geological Society, Occasional Publications series, v. 7, p. 147–64.

Ratcliffe, K.T., Hughes, A.D., Lawton, D.E., Wray, D.S., Bessa, F., Pearce, T.J. and Martin. J. 2006. A regional chemostratigraphically-defined correlation framework for the late TAG-I in Blocks 402 and 405a, Algeria. Petroleum Geoscience, v. 12, p. 3–12.

Ratcliffe, K.T., Morton, A., Ritcey, D. and Evenchick, C.E. 2007. Whole rock geochemistry and heavy mineral analysis as exploration tools in the Bowser and Sustut Basins, British Colombia, Canada. Journal of Canadian Petroleum Geology, v. 55, p. 320–37.

Ratcliffe, K.T., Wright, A.M., Montgomery, P. Palfrey, A. Vonk, A. Vermeulen, J. and Barrett, Fig. 5. Eigen vector 1 (EV1) vs. Eigen vector 1 (EV2) calculated from data in the Haynesville Formation M. 2010. Application of chemostratigraphy to from well George T.W GUA-8H. Elements fall into three broad groupings reflecting their mineralogical the Mungaroo Formation, the Gorgon Field, associations in the formation.

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